Stupples shot a 5-under 67 over the Mission Hills course. Ochoa, who is trying to win her second straight major title, shared second place with Ai Miyazato at 68.
Natalie Gulbis and Heather Young were tied for third at 69. Mi Hyun Kim, Liselotte Neumann, Maria Hjorth and amateur Maria Jose Uribe were all at 70, and the group at 71 included Annika Sorenstam, Paula Creamer and defending champion Morgan Pressel.
Ochoa is seeking her third tournament title of 2008. She broke through with her first major championship last summer when she won the Women's British Open.
Stupples, 34, gave birth to her first child last year and her game has only recently returned to winning form.
"All of a sudden it came back almost overnight," she said, "and that was really good to see. The rustiness I felt at the end of last year when I came back was with my short game. I managed to work that out, so I'm really excited and ready to play."